80 Papers from the Department of Marine Biology. 



soft flesh of the disc or b}^ clasping the pinnules or arms of the crinoid. 

 The chelae are less effective for maintaining a hold than the thoracic 

 legs, but it is to be noticed that these can not be said to be specially 

 modified for this purpose. They are provided with two sharp claws, 

 but this provision is also made in cases where the alpheid has no such 

 commensal habits. 



When removed from the crinoids they swim about very rapidly, but 

 return as soon as possible to the shelter of the host, and cling to it as 

 before. They exhibit reactions to light and touch in a very marked 

 manner. Alpheids placed in a glass vessel always cluster together on 

 the side of the vessel opposite from the light. Besides being negatively 

 heliotropic, they are strongly thigmotropic, for when the finger is 

 introduced into the water it is instantly embraced by the thoracic legs 

 of the alpheid. In the absence of any foreign object, the alpheids 

 embrace one another, so that a number left together in a vessel soon 

 look like a mass of swarming bees. 



There seems to be a limited faculty of colour change. One individual 

 with wide stripes of pigment became lighter toward night, darker again 

 at day. Unfortunately I did not make any extended observations on 

 this point. 



Synalpheus comatularum (Haswell). (Plate 1, Fig. 1.) 



Alpheus comatularum, HASWELL, Proc. Linn. Soc., N. S. Wales, vol. 6; Catalogue of the Australian 

 Stalk and Sessile Eyed Crustacea, Australian Mus., pp. 189-90. 



This species was dredged in a few fathoms of water in Albany Passage, 

 near Cape York, during the cruise of H. M. S. Alert. "They were 

 invariably found clinging to the arms of a species of comatulid to which 

 their markings gave them a general resemblance." It was also obtained 

 during the voyage of the Challenger, in neighbouring waters and off 

 Ceylon, by Professor Herdman. 



We did not find this form at Murray Island, but during a visit to 

 the western Islands of Torres Straits, in the early days of November, I 

 obtained it in 3 to 5 fathoms off the great reefs lying north of Mabuiag 

 Island. With the greatest kindness, Mr. Walker, managing director 

 of the Papuan Industries Co., Ltd., put the company's schooner Dogai 

 at my disposal and, with three divers from Badu in addition to the 

 ordinary crew, I spent a couple of days on the Mabuiag pearling grounds. 

 For an hour or more at slack tide the most wonderful crinoids were to be 

 collected by diving. The species so common at Murray Island (Coman- 

 thus annulatum) was the dominant form here, but represented by indi- 

 viduals even larger and more splendid in colour than those inhabiting 

 the reefs of the Murray Islands. 



S. comatularum is markedly larger than S. brucei and is stouter in 

 general appearance. But the resemblance in colouration and habits is 

 so close as to suggest specific identity until the peculiar form of the 



